Process for eliminating arsenic and antimony from iron ores and manganese ores



Patented Aug. 22, 1933 UNlTED STATES PROCESS FOR ELIMIINATING ARSENIC AND ANTIM GANESE onus ONY FROM IRON ORES MAN- Erich Scheil,- Dortmund, Germany, assignor to the firm Vereinlste Stahlwerke Aktiengesellschaft, Dusseldorf, Germany:

No Drawing. Application February 8,

Serial Nissan-:59, 9, 1931 7Claims.

It has been tried to eliminate arsenic from ores containing it by allowing carbonic acid to pass over them. This process has a'certain de-- gree of success only in the case of a very limited number of ores. It is only successful if the arsenic is present in a form suitable for the elimination, this form being probably arsenides.

In the case of most ores the problem is therefore to convert the arsenic compound first into a form which is suitable for the expulsion of arsenic. As Mathesius and Diekman have shown this process succeeds by reducing the ore with hydrogen and so bringing the arsenic compounds into a condition .wherein the arsenic can be expelled by carbonic acid. Schumacher tried to obtain the same result by an alternating treatment with waste gases and combustible gases.

It has been found that there is no need for this multiple treatment but that the arsenic can be eliminated by one only gas mixture, ifcertain conditions are compliedwith.

The present invention is based upon the observation that the conversion by means of carbon monoxide of the arsenic compounds into the form which is suitable for the elimination of arsenic begins already with gases containing far less carbon monoxide than is required for the reduction of iron oxides to metallic iron. While therefore a gas mixture according to the present invention will reduce the existing iron oxides at most to iron oxide (FeO), there occurs already a reduction of the arsenic compounds existingin the ore to a formwhich facilitates the expulsion of arsenic, probably FeAs. The reduced part of the arsenic compound is thereupon split by the action of the carbonic acid which is present in the gas mixture, probably according to the equation:

The arsenic escapes in the form of gas together with the'gas mixture and can thus be eliminated from the ore. In order to avoid the danger of a retrogressive process, suitable measures must be taken to exhaust the gases which were used in the treatment. The carbon monoxide contents of the gas mixture can be replaced entirely or partly by other reducing agents such as, for example, hydrogen or hydrocarbons. The carbonic acid, on the other hand, is an essential constituent of the gas mixture and is necessary for obtaining the elimination of the arsenic.

' The upper limit of the carbon monoxide contents of the gas according to the present invention, is determined by the condition that the and in Germany February ore at that stage must not yet form any metallic iron or iron carbides. The iron probably absorbs a part of the gasiform arsenic as mixed crystals. As, however, the content of the gas in carbonic acids is not large enough to re-oxidize the mixed crystal, this part of the arsenic is retained in the ore.

The limit of the gas mixtures, in the presence of which no free iron is yet separated, has been established in the case 01. mixtures of carbon monoxide and carbonic acid by the tests carried out by R. Scherik and other collaborators; see Ze'itschrift fiir anorganische und allgemelne Chemie, No. 167 (1927) page 316. In Figure 1 of this work the curve of equilibrium is given for FeO and metallic iron. The efiect of pressure and temperature is also stated in this article. The presence of lime, silicic acid and the like displaces this limit, and this displacement can be measured by simple methods and known to any expert, for instance the displacement oi. the equilibrium between carbon monoxide and carbon dioxide over iron oxides. by the presence of lime, silica etc. may be determined by leading several mixtures of carbon monoxide and carbon dioxide over the mixture of the finely pulverized ore heated to a certain temperature. After a certain period in which the gas mixture acted upon the ore, said period depending upon the temperature and amounting to about 4 hours at 900 C., the iron oxides present in the mixture are to be ascertained.

In the table which is annexed As-content oi the ore in Sb-content of the ore in Gas mixture After e the the treatment After the treatment oo coi arses grasses are found, as examples for this process, the results obtained by treating an ore containing 0.73% As and 1.3% Sb at a temperature of 900 C Ior one hour. The most favourable results were obtained with mixtures containing between and 80% CO2, the remainder being C0, in one case, and 70-90% C02, the remainder being H2,

' carbon monoxide-carbonic acid mixtures, the CO:

contents to about -70%. The more hydrogen is present, the more does the most favourable mixture show a higher content of CO2. It is still better to increase gradually the 00: contents of the gas during the time allowed for its action and in this the carbonic acid contents may reach 100% towards the end of the process.

The lower limit of the temperature during the process is established by the reaction velocity, so that temperatures below 500 are not suitable. As regards the upper limit, it is advisable not to get too near the temperature at which sintering occurs. This point diflers according to the various ores but is, on the average, about 1000.

Gases which are suitable for carrying out the process are: waste gases from furnaces, blast furnace gas, coking oven gas, waste gases from lime kilns etc. In general the required CO: contents of the gas are not reached and the balance must be added. The presence of nitrogen affects the process only inasmuch as it lowers the partial pressure.

Besides arsenic, antimony can be eliminated by the same process. The reaction, all other conditions being equal, must, however, be protracted a little. Furthermore, the elimination of arsenic and antimony according to this process, is successful not only in the case of iron ores but also in the case of manganese ores.

What I claim and desire to secure by Letters Patent is:-

1. Process for the elimination of arsenic and antimony from iron and manganese ores, consisting in heating the ore to a high temperature and then bringing it into contact with a mixture of carbonic acid and a reducing gas, the quantity of the mixture used being insufllcient at the temperature used to reduce the ore to metal.

2. Process for the elimination of arsenic and antimony from iron and manganese ores, consisting in heating theore above 500 C. and then bringing it into contact with a mixture of carbonic acid and a reducing gas, the quantity of the mixture used being insuilicient at the temperature used to reduce the ore to metal.

3. Process for the elimination of arsenic and antimony from iron and manganese ores, consisting in heating the ore to a high temperature and then bringing it into contact with a mixture of carbonic acid and carbon monoxide, the quantity of the mixture used being insuflicient at the temperature used to reduce the ore to metal.

4. Process for the elimination of arsenic and antimony from iron and manganese ores, consisting in heating the ore to a high temperature and then bringing it into contact with a mixture of carbonic acid and hydrogen the quantity of the mixture used being insumcient at the temperature used to reduce the ore to metal.

5. Process for the elimination of arsenic and antimony from iron and manganese ores, consisting in heating the ore to a high temperature and then bringing it into contact with a mixture of carbonic acid and a hydrocarbon the quantity of the mixture used being insuflicient at the temperature used to reduce the ore to metal.

6. Process for the elimination of arsenic and antimony from iron and manganese ores, consisting in heating the ore to a high temperature and then bringing it into contact with a mixture of carbonic acid and a reducing gas, the quantity of the mixture used being insuflicient at the temperature used to reduce the ore to metal, and the carbonic acid content of the mixture being gradually brought up to its desired maximum ERICH SCH'EIL. 

